LATA1, a RING E3 ligase, modulates the tiller angle by affecting auxin asymmetric distribution and content in rice.

The tiller angle is an important agronomic trait that determines plant architecture and grain yield in rice (Oryza sativa L.). However, the molecular regulation mechanism of the rice tiller angle remains unclear. Here, we identified a rice tiller angle gene, LARGE TILLER ANGLE 1 (LATA1), using the MutMap approach. LATA1 encodes a C3H2C3-type RING zinc finger E3 ligase and the conserved region of the RING zinc finger is essential for its E3 activity. LATA1 was highly expressed in the root and tiller base and LATA1-GFP fusion protein was specifically localized to the nucleus. The mutation of LATA1 significantly reduced indole-3-acetic acid content and attenuated lateral auxin transport, thereby resulting in defective shoot gravitropism and spreading plant architecture in rice. Further investigations found that LATA1 may indirectly affect gravity perception by modulating the sedimentation rate of gravity-sensing amyloplasts upon gravistimulation. Our findings provide new insights into the molecular mechanism underlying the rice tiller angle and new genetic resource for the improvement of plant architecture in rice.

Rice florigens control a common set of genes at the shoot apical meristem including the F-BOX BROADER TILLER ANGLE 1 that regulates tiller angle and spikelet development.

Rice flowering is triggered by transcriptional reprogramming at the shoot apical meristem (SAM) mediated by florigenic proteins produced in leaves in response to changes in photoperiod. Florigens are more rapidly expressed under short days (SDs) compared to long days (LDs) and include the HEADING DATE 3a (Hd3a) and RICE FLOWERING LOCUS T1 (RFT1) phosphatidylethanolamine binding proteins. Hd3a and RFT1 are largely redundant at converting the SAM into an inflorescence, but whether they activate the same target genes and convey all photoperiodic information that modifies gene expression at the SAM is currently unclear. We uncoupled the contribution of Hd3a and RFT1 to transcriptome reprogramming at the SAM by RNA sequencing of dexamethasone-inducible over-expressors of single florigens and wild-type plants exposed to photoperiodic induction. Fifteen highly differentially expressed genes common to Hd3a, RFT1, and SDs were retrieved, 10 of which still uncharacterized. Detailed functional studies on some candidates revealed a role for LOC_Os04g13150 in determining tiller angle and spikelet development and the gene was renamed BROADER TILLER ANGLE 1 (BRT1). We identified a core set of genes controlled by florigen-mediated photoperiodic induction and defined the function of a novel florigen target controlling tiller angle and spikelet development.

M2 plants derived from different tillers of a chemically mutagenized rice M1 plant carry independent sets of mutations.

Generation of mutant populations with high genetic diversity is key for mutant screening and crop breeding. For this purpose, the single-seed descent method, in which one mutant line is established from a single mutagenized seed, is commonly used. This method ensures the independence of the mutant lines, but the size of the mutant population is limited because it is no greater than the number of fertile M1 plants. The rice mutant population size can be increased if a single mutagenized plant produces genetically independent siblings. Here, we used whole-genome resequencing to examine the inheritance of mutations from a single ethyl methanesulfonate (EMS)-mutagenized seed (M1 ) of Oryza sativa in its progeny (M2 ). We selected five tillers from each of three M1 plants. A single M2 seed was selected from each tiller, and the distributions of mutations induced by EMS were compared. Surprisingly, in most pairwise combinations of M2 siblings from the same parent, ≥85.2-97.9% of all mutations detected were not shared between the siblings. This high percentage suggests that the M2 siblings were derived from different cells of the M1 embryo and indicates that several genetically independent lines can be obtained from a single M1 plant. This approach should allow a large reduction in the number of M0 seeds needed to obtain a mutant population of a certain size in rice. Our study also suggests that multiple tillers of a rice plant originate from different cells of the embryo.

OsCSN2 orchestrates Oryza sativa L. growth and development through modulation of the GA and BR pathways.

The COP9 signalosome (CSN) is a conserved protein complex found in higher eukaryotes, consisting of eight subunits, and it plays a crucial role in regulating various processes of plant growth and development. Among these subunits, CSN2 is one of the most conserved components within the COP9 signalosome complex. Despite its prior identification in other species, its specific function in Oryza sativa L. (Rice) has remained poorly understood. In this study, we investigated the role of CSN2 in rice using gene editing CRISPR/Cas9 technology and overexpression techniques. We created two types of mutants: the oscsn2 mutant and the OsCSN2-OE mutant, both in the background of rice, and also generated point mutants of OsCSN2 (OsCSN2K64E, OsCSN2K67E, OsCSN2K71E and OsCSN2K104E) to further explore the regulatory function of OsCSN2. Phenotypic observation and gene expression analysis were conducted on plants from the generated mutants, tracking their growth from the seedling to the heading stages. The results showed that the loss and modification of OsCSN2 had limited effects on plant growth and development during the early stages of both the wild-type and mutant plants. However, as the plants grew to 60 days, significant differences emerged. The OsCSN2 point mutants exhibited increased tillering compared to the OsCSN2-OE mutant plants, which were already at the tillering stage. On the other hand, the OsCSN2 point mutant had already progressed to the heading and flowering stages, with the shorter plants. These results, along with functional predictions of the OsCSN2 protein, indicated that changes in the 64th, 67th, 71st, and 104th amino acids of OsCSN2 affected its ubiquitination site, influencing the ubiquitination function of CSN and consequently impacting the degradation of the DELLA protein SLR1. Taken together, it can be speculated that OsCSN2 plays a key role in GA and BR pathways by influencing the functional regulation of the transcription factor SLR1 in CSN, thereby affecting the growth and development of rice and the number of tillers.

Alleles on locus chromosome 4B from different parents confer tiller number and the yield-associated traits in wheat.

Pleiotropy is frequently detected in agronomic traits of wheat (Triticum aestivum). A locus on chromosome 4B, QTn/Ptn/Sl/Sns/Al/Tgw/Gl/Gw.caas-4B, proved to show pleiotropic effects on tiller, spike, and grain traits using a recombinant inbred line (RIL) population of Qingxinmai × 041133. The allele from Qingxinmai increased tiller numbers, and the allele from line 041133 produced better performances of spike traits and grain traits. Another 52 QTL for the eight traits investigated were detected on 18 chromosomes, except for chromosomes 5D, 6D, and 7B. Several genes in the genomic interval of the locus on chromosome 4B were differentially expressed in crown and inflorescence samples between Qingxinmai and line 041133. The development of the KASP marker specific for the locus on chromosome 4B is useful for molecular marker-assisted selection in wheat breeding.

Natural variation in the Tn1a promoter regulates tillering in rice.

Rice tillering is an important agronomic trait that influences plant architecture and ultimately affects yield. This can be genetically improved by mining favourable variations in genes associated with tillering. Based on a previous study on dynamic tiller number, we cloned the gene Tiller number 1a (Tn1a), which encodes a membrane-localised protein containing the C2 domain that negatively regulates tillering in rice. A 272 bp insertion/deletion at 387 bp upstream of the start codon in the Tn1a promoter confers a differential transcriptional response and results in a change in tiller number. Moreover, the TCP family transcription factors Tb2 and TCP21 repress the Tn1a promoter activity by binding to the TCP recognition site within the 272 bp indel. In addition, we identified that Tn1a may affect the intracellular K+ content by interacting with a cation-chloride cotransporter (OsCCC1), thereby affecting the expression of downstream tillering-related genes. The Tn1a+272 bp allele, associated with high tillering, might have been preferably preserved in rice varieties in potassium-poor regions during domestication. The discovery of Tn1a is of great significance for further elucidating the genetic basis of tillering characteristics in rice and provides a new and favourable allele for promoting the geographic adaptation of rice to soil potassium.

Photosynthesis regulates tillering bud elongation and nitrogen-use efficiency via sugar-induced NGR5 in rice.

Rice tillering is one of the most important agronomical traits largely determining grain yield. Photosynthesis and nitrogen availability are two important factors affecting rice tiller bud elongation; however, underlying mechanism and their cross-talk is poorly understood. Here, we used map-based cloning, transcriptome profiling, phenotypic analysis, and molecular genetics to understand the roles of the Decreased Tiller Number 1 (DTN1) gene that encodes the fructose-1,6-bisphosphate aldolase and involves in photosynthesis required for light-induced axillary bud elongation in rice. Deficiency of DTN1 results in the reduced photosynthetic rate and decreased contents of sucrose and other sugars in both leaves and axillary buds, and the reduced tiller number in dtn1 mutant could be partially rescued by exogenous sucrose treatment. Furthermore, we found that the expression of nitrogen-mediated tiller growth response 5 (NGR5) was remarkably decreased in shoot base of dtn1-2, which can be activated by sucrose treatment. Overexpression of NGR5 in the dtn1-2 could partially rescue the reduced tiller number, and the tiller number of dtn1-2 was insensitive to nitrogen supply. This work demonstrated that the sugar level regulated by photosynthesis and DTN1 could positively regulate NGR5 expression, which coordinates the cross-talk between carbon and nitrate to control tiller bud outgrowth in rice.

Knockout of the sugar transporter OsSTP15 enhances grain yield by improving tiller number due to increased sugar content in the shoot base of rice (Oryza sativa L.).

Sugar transporter proteins (STPs) play critical roles in regulating plant stress tolerance, growth, and development. However, the role of STPs in regulating crop yield is poorly understood. This study elucidates the mechanism by which knockout of the sugar transporter OsSTP15 enhances grain yield via increasing the tiller number in rice. We found that OsSTP15 is specifically expressed in the shoot base and vascular bundle sheath of seedlings and encodes a plasma membrane-localized high-affinity glucose efflux transporter. OsSTP15 knockout enhanced sucrose and trehalose-6-phosphate (Tre6P) synthesis in leaves and improved sucrose transport to the shoot base by inducing the expression of sucrose transporters. Higher glucose, sucrose, and Tre6P contents were observed at the shoot base of stp15 plants. Transcriptome and metabolome analyses of the shoot base demonstrated that OsSTP15 knockout upregulated the expression of cytokinin (CK) synthesis- and signaling pathway-related genes and increased CK levels. These findings suggest that OsSTP15 knockout represses glucose export from the cytoplasm and simultaneously enhances sugar transport from source leaves to the shoot base by promoting the synthesis of sucrose and Tre6P in leaves. Subsequent accumulation of glucose, sucrose, and Tre6P in the shoot base promotes tillering by stimulating the CK signaling pathway.

Zaxinone Synthase overexpression modulates rice physiology and metabolism, enhancing nutrient uptake, growth and productivity.

The rice Zaxinone Synthase (ZAS) gene encodes a carotenoid cleavage dioxygenase (CCD) that forms the apocarotenoid growth regulator zaxinone in vitro. Here, we generated and characterized constitutive ZAS-overexpressing rice lines, to better understand ZAS role in determining zaxinone content and regulating growth and architecture. ZAS overexpression enhanced endogenous zaxinone level, promoted root growth and increased the number of productive tillers, leading to about 30% higher grain yield per plant. Hormone analysis revealed a decrease in strigolactone (SL) content, which we confirmed by rescuing the high-tillering phenotype through application of a SL analogue. Metabolomics analysis revealed that ZAS overexpressing plants accumulate higher amounts of monosaccharide sugars, in line with transcriptome analysis. Moreover, transgenic plants showed higher carbon (C) assimilation rate and elevated root phosphate, nitrate and sulphate level, enhancing the tolerance towards low phosphate (Pi). Our study confirms ZAS as an important determinant of rice growth and architecture and shows that ZAS regulates hormone homoeostasis and a combination of physiological processes to promote growth and grain yield, which makes this gene an excellent candidate for sustainable crop improvement.

Insertion of a miniature inverted-repeat transposable element into the promoter of OsTCP4 results in more tillers and a lower grain size in rice.

A class I PCF type protein, TCP4, was identified as a transcription factor associated with both grain size and tillering through a DNA pull-down-MS assay combined with a genome-wide association study. This transcription factor was found to have a significant role in the variations among the 533 rice accessions, dividing them into two main subspecies. A Tourist-like miniature inverted-repeat transposable element (MITE) was discovered in the promoter of TCP4 in japonica/geng accessions (TCP4M+), which was found to suppress the expression of TCP4 at the transcriptional level. The MITE-deleted haplotype (TCP4M-) was mainly found in indica/xian accessions. ChIP-qPCR and EMSA demonstrated the binding of TCP4 to promoters of grain reservoir genes such as SSIIa and Amy3D in vivo and in vitro, respectively. The introduction of the genomic sequence of TCP4M+ into different TCP4M- cultivars was found to affect the expression of TCP4 in the transgenic rice, resulting in decreased expression of its downstream target gene SSIIa, increased tiller number, and decreased seed length. This study revealed that a Tourist-like MITE contributes to subspecies divergence by regulating the expression of TCP4 in response to environmental pressure, thus influencing source-sink balance by regulating starch biosynthesis in rice.

Determining nitrogen topdressing rates in accordance with actual seedling density and crop nitrogen status in direct-seeded rice.

BACKGROUND: Adjusting nitrogen (N) input based on actual seedling density (ASD) and plant N status is a practical approach for improving the yield stability of direct-seeded rice. However, the adjustment of topdressing N rates has been empirical in the past. This study aimed to establish a quantitative approach for determining N topdressing rates during tillering (Ntil ) and panicle development (NPI ) based on ASD and crop N status in direct-seeded rice. Field experiments were conducted involving 12 treatments, consisting of four Ntil and three seeding rates in 2017, and eight treatments combining seeding rate, Ntil , and NPI in 2020. RESULTS: Linear regression analysis revealed that the tiller number at panicle initiation (TILPI ) was predominantly influenced by ASD and Ntil . The determination coefficients (R2 ) of the regression models ranged from 0.887 to 0.936 across the four-season experiments. The results indicated that Ntil could be determined accurately using ASD and the target maximum tiller number. Similarly, grain yield was influenced significantly by the N uptake at panicle initiation (NUPPI ) and NPI , with R2 of 0.814 and 0.783 in the early and late seasons of 2020, respectively. This suggested that NPI could be calculated based on NUPPI and the target grain yield. CONCLUSION: The findings offer a quantitative method for establishing N topdressing rates for tillering and panicle development, relying on the monitoring of actual seedling density and plant N status in direct-seeded rice production. © 2023 Society of Chemical Industry.

BTA2 regulates tiller angle and the shoot gravity response through controlling auxin content and distribution in rice.

Tiller angle is a key agricultural trait that establishes plant architecture, which in turn strongly affects grain yield by influencing planting density in rice. The shoot gravity response plays a crucial role in the regulation of tiller angle in rice, but the underlying molecular mechanism is largely unknown. Here, we report the identification of the BIG TILLER ANGLE2 (BTA2), which regulates tiller angle by controlling the shoot gravity response in rice. Loss-of-function mutation of BTA2 dramatically reduced auxin content and affected auxin distribution in rice shoot base, leading to impaired gravitropism and therefore a big tiller angle. BTA2 interacted with AUXIN RESPONSE FACTOR7 (ARF7) to modulate rice tiller angle through the gravity signaling pathway. The BTA2 protein was highly conserved during evolution. Sequence variation in the BTA2 promoter of indica cultivars harboring a less expressed BTA2 allele caused lower BTA2 expression in shoot base and thus wide tiller angle during rice domestication. Overexpression of BTA2 significantly increased grain yield in the elite rice cultivar Huanghuazhan under appropriate dense planting conditions. Our findings thus uncovered the BTA2-ARF7 module that regulates tiller angle by mediating the shoot gravity response. Our work offers a target for genetic manipulation of plant architecture and valuable information for crop improvement by producing the ideal plant type.

The TaGW2-TaSPL14 module regulates the trade-off between tiller number and grain weight in wheat.

IDEAL PLANT ARCHITECTURE1 (IPA1) is a pivotal gene controlling plant architecture and grain yield. However, little is known about the effects of Triticum aestivum SQUAMOSA PROMOTER-BINDING-LIKE 14 (TaSPL14), an IPA1 ortholog in wheat, on balancing yield traits and its regulatory mechanism in wheat (T. aestivum L.). Here, we determined that the T. aestivum GRAIN WIDTH2 (TaGW2)-TaSPL14 module influences the balance between tiller number and grain weight in wheat. Overexpression of TaSPL14 resulted in a reduced tiller number and increased grain weight, whereas its knockout had the opposite effect, indicating that TaSPL14 negatively regulates tillering while positively regulating grain weight. We further identified TaGW2 as a novel interacting protein of TaSPL14 and confirmed its ability to mediate the ubiquitination and degradation of TaSPL14. Based on our genetic evidence, TaGW2 acts as a positive regulator of tiller number, in addition to its known role as a negative regulator of grain weight, which is opposite to TaSPL14. Moreover, combinations of TaSPL14-7A and TaGW2-6A haplotypes exhibit significantly additive effects on tiller number and grain weight in wheat breeding. Our findings provide insight into how the TaGW2-TaSPL14 module regulates the trade-off between tiller number and grain weight and its potential application in improving wheat yield.

OsSPL14 acts upstream of OsPIN1b and PILS6b to modulate axillary bud outgrowth by fine-tuning auxin transport in rice.

As a multigenic trait, rice tillering can optimize plant architecture for the maximum agronomic yield. SQUAMOSA PROMOTER BINDING PROTEIN-LIKE14 (OsSPL14) has been demonstrated to be necessary and sufficient to inhibit rice branching, but the underlying mechanism remains largely unclear. Here, we demonstrated that OsSPL14, which is cleaved by miR529 and miR156, inhibits tillering by fine-tuning auxin transport in rice. RNA interference of OsSPL14 or miR529 and miR156 overexpression significantly increased the tiller number, whereas OsSPL14 overexpression decreased the tiller number. Histological analysis revealed that the OsSPL14-overexpressing line had normal initiation of axillary buds but inhibited outgrowth of tillers. Moreover, OsSPL14 was found to be responsive to indole-acetic acid and 1-naphthylphthalamic acid, and RNA interference of OsSPL14 reduced polar auxin transport and increased 1-naphthylphthalamic acid sensitivity of rice plants. Further analysis revealed that OsSPL14 directly binds to the promoter of PIN-FORMED 1b (OsPIN1b) and PIN-LIKE6b (PILS6b) to regulate their expression positively. OsPIN1b and PILS6b were highly expressed in axillary buds and proved involved in bud outgrowth. Loss of function of OsPIN1b or PILS6b increased the tiller number of rice. Taken together, our findings suggested that OsSPL14 could control axillary bud outgrowth and tiller number by activating the expression of OsPIN1b and PILS6b to fine-tune auxin transport in rice.

Molecular characterization reveals that OsSAPK3 improves drought tolerance and grain yield in rice.

BACKGROUND: Many data suggest that the sucrose non-fermenting 1-related kinases 2 (SnRK2s) are very important to abiotic stress for plants. In rice, these kinases are known as osmotic stress/ABA-activated protein kinases (SAPKs). Osmotic stress/ABA-activated protein kinase 3 (OsSAPK3) is a member of SnRK2II in rice, but its function is still unclear. RESULTS: The expression of OsSAPK3 was up regulated by drought, NaCl, PEG and ABA. OsSAPK3 mutated seedings (sapk3-1 and sapk3-2) showed reduced hypersensitivity to exogenous ABA. In addition, under drought conditions, sapk3-1 and sapk3-2 showed more intolerance to drought, including decreased survival rate, increased water loss rate, increased stomatal conductance and significantly decreased expression levels of SLAC1 and SLAC7. Physiological and metabolic analyses showed that OsSAPK3 might play an important role in drought stress signaling pathway by affecting osmotic adjustment and osmolytes, ROS detoxification and expression of ABA dependent and independent dehydration-responsive genes. All gronomic traits analyses demonstrated that OsSAPK3 could improve rice yield by affecting the regulation of tiller numbers and grain size. CONCLUSION: OsSAPK3 plays an important role in both ABA-dependent and ABA-independent drought stress responses. More interestingly, OsSAPK3 could improve rice yield by indirectly regulating tiller number and grain size. These findings provide new insight for the development of drought-resistant rice.

Different contributions of PROG1 and TAC1 to the angular kinematics of the main culm and tillers of wild rice (Oryza rufipogon).

MAIN CONCLUSION: PROG1 is necessary but insufficient for the main culm inclination while TAC1 partially takes part in it, and both genes promote tiller inclination in Asian wild rice. Asian wild rice (Oryza rufipogon), the ancestor of cultivated rice (O. sativa), has a prostrate architecture, with tillers branching from near the ground. The main culm of each plant grows upward and then tilts during the vegetative stage. Genes controlling tiller angle have been reported; however, their genetic contributions to the culm movement have not been quantified. Here, we quantified their genetic contributions to angular kinematics in the main culm and tillers. For the main culm inclination, one major QTL surrounding the PROG1 region was found. In cultivated rice, tillers firstly inclined and lately rose, while it kept inclining in wild rice. It was suggested that PROG1 affected the tiller elevation angle in the later kinematics, whereas TAC1 was weakly associated with the tiller angle in the whole vegetative stage. Micro-computed tomography (micro-CT) suggested that these angular changes are produced by the bending of culm bases. Because near-isogenic lines (NILs) of wild rice-type Prog1 and Tac1 alleles in the genetic background of cultivated rice did not show the prostrate architecture, the involvement of another gene(s) for inclination of the main culm was suggested. Our findings will not only contribute to the understanding of the morphological transition during domestication but also be used in plant breeding to precisely reproduce the ideal plant architecture by combining the effects of multiple genes.

Natural variation in Tiller Number 1 affects its interaction with TIF1 to regulate tillering in rice.

Tiller number per plant-a cardinal component of ideal plant architecture-affects grain yield potential. Thus, alleles positively affecting tillering must be mined to promote genetic improvement. Here, we report a Tiller Number 1 (TN1) protein harbouring a bromo-adjacent homology domain and RNA recognition motifs, identified through genome-wide association study of tiller numbers. Natural variation in TN1 affects its interaction with TIF1 (TN1 interaction factor 1) to affect DWARF14 expression and negatively regulate tiller number in rice. Further analysis of variations in TN1 among indica genotypes according to geographical distribution revealed that low-tillering varieties with TN1-hapL are concentrated in Southeast Asia and East Asia, whereas high-tillering varieties with TN1-hapH are concentrated in South Asia. Taken together, these results indicate that TN1 is a tillering regulatory factor whose alleles present apparent preferential utilization across geographical regions. Our findings advance the molecular understanding of tiller development.

Rice DSP controls stigma, panicle and tiller primordium initiation.

Tiller and seed number are key determinants of rice (Oryza sativa) yield. These traits are mainly affected by tiller, panicle, spikelet and stigma formation, but to date, no single gene involved in the development of all these organs has been identified. Here, we found a rice mutant defective stigma and panicle (dsp) with greatly reduced numbers of tillers and panicle branches, and ovaries lacking stigmas, due to defects in primordium initiation. We cloned DSP using sequencing-based mapping and verified its function with the CRISPR/Cas9 system. DSP encodes a transcription factor containing an APETALA2/ETHYLENE RESPONSE FACTOR (AP2/ERF) domain that recognizes the GCC motif and a transcription-activating domain at the site of 244-314 that contains an angiosperm-related (AR) motif. Mutating the AR motif resulted in the dsp mutant phenotypes, whereas mutating the AP2/ERF domain led to seedling death. DSP directly regulated PINOID (PID) expression to determine the emergence of rice stigmas, and PID overexpression partially rescued the stigma defect in the dsp cr2-8 and dsp mutants. Moreover, DSP indirectly affected LAX PANICLE1 (LAX1) expression to determine tiller primordium formation and synergistically regulated panicle primordium development. Our results indicated that DSP was a key regulator that modulated different genetic pathways to control the initiation of stigma primordia, the axillary meristem formation of tillers and panicle branches, which revealed their molecular mechanisms and cross-networks, laying the vital foundation for rice yield and trait improvement.

A HST1-like gene controls tiller angle through regulating endogenous auxin in common wheat.

Tiller angle is one of the most important agronomic traits and one key factor for wheat ideal plant architecture, which can both increase photosynthetic efficiency and greatly enhance grain yield. Here, a deacetylase HST1-like (TaHST1L) gene controlling wheat tiller angle was identified by the combination of a genome-wide association study (GWAS) and bulked segregant analysis (BSA). Ethyl methane sulfonate (EMS)-mutagenized tetraploid wheat lines with the premature stop codon of TaHST1L exhibited significantly smaller tiller angles than the wild type. TaHST1L-overexpressing (OE) plants exhibited significantly larger tiller angles and increased tiller numbers in both winter and spring wheat, while TaHST1L-silenced RNAi plants displayed significantly smaller tiller angles and decreased tiller numbers. Moreover, TaHST1L strongly interacted with TaIAA17 and inhibited its expression at the protein level, and thus possibly improved the content of endogenous auxin in the basal tissue of tillers. The transcriptomics and metabolomics results indicated that TaHST1L might change plant architecture by mediating auxin signal transduction and regulating endogenous auxin levels. In addition, a 242-bp insertion/deletion (InDel) in the TaHST1L-A1 promoter altered transcriptional activity and TaHST1L-A1b allele with the 242-bp insertion widened the tiller angle of TaHST1L-OE transgenic rice plants. Wheat varieties with TaHST1L-A1b allele possessed the increased tiller angle and grain yield. Further analysis in wheat and its progenitors indicated that the 242-bp InDel possibly originated from wild emmer and was strongly domesticated in the current varieties. Therefore, TaHST1L involved in the auxin signalling pathway showed the big potential to improve wheat yield by controlling plant architecture.

LAZY3 interacts with LAZY2 to regulate tiller angle by modulating shoot gravity perception in rice.

Starch biosynthesis in gravity-sensing tissues of rice shoot determines the magnitude of rice shoot gravitropism and thus tiller angle. However, the molecular mechanism underlying starch biosynthesis in rice gravity-sensing tissues is still unclear. We characterized a novel tiller angle gene LAZY3 (LA3) in rice through map-based cloning. Biochemical, molecular and genetic studies further demonstrated the essential roles of LA3 in gravity perception of rice shoot and tiller angle control. The shoot gravitropism and lateral auxin transport were defective in la3 mutant upon gravistimulation. We showed that LA3 encodes a chloroplast-localized tryptophan-rich protein associated with starch granules via Tryptophan-rich region (TRR) domain. Moreover, LA3 could interact with the starch biosynthesis regulator LA2, determining starch granule formation in shoot gravity-sensing tissues. LA3 and LA2 negatively regulate tiller angle in the same pathway acting upstream of LA1 to mediate asymmetric distribution of auxin. Our study defined LA3 as an indispensable factor of starch biosynthesis in rice gravity-sensing tissues that greatly broadens current understanding in the molecular mechanisms underlying the starch granule formation in gravity-sensing tissues, and provides new insights into the regulatory mechanism of shoot gravitropism and rice tiller angle.